The present invention is in the field of imaging systems. More particularly, the present invention provides a method and apparatus for holding recording media against a media support surface of an imaging system using an arrangement of variable cross-section vacuum grooves.
In many imaging systems, such as imagesetters or platesetters, a movable optical carriage is used to displace a laser system or other imaging source in a slow scan direction along a curved or planar media support surface (e.g., flatbed, internal drum, external drum, or other support surface). The imaging source exposes a supply of recording media supported on, and held against, the media support surface. Generally, the imaging source includes an optical system for scanning one or more laser or other radiation beams modulated by an information signal over the recording media to record an image onto the recording media. For example, in an internal drum recording system, the imaging source may include a beam deflection assembly, comprising a deflector element (e.g., a mirror) and a spin motor for rotating the deflector element, wherein the beam deflection assembly deflects an imaging beam generated by a radiation source across the recording media.
The recording media to be imaged by an imaging system is commonly supplied in web form or in discrete sheets or plates. The recording media may comprise a photosensitive, radiation sensitive, thermally sensitive, or other type of imageable material. In a given imaging system, different size recording media may be used for different applications, depending on such factors as the type of image to be scanned, etc. Regardless of the size of the recording media that is used, however, it is important to hold the recording media firmly against the media support surface. Any lifting of the recording media away from the media support surface may result in an out of focus image on the recording media. This may be due, for example, to the fixed and short focal depth of the imaging beam., as well as other factors.
In many imaging systems, a vacuum system is employed to hold the recording media against the media support surface. Commonly, the vacuum system operates by drawing a vacuum through a plurality of vacuum ports, disposed over the media support surface, which draw air from a plurality of constant cross-section (e.g., constant depth and width) vacuum grooves. When a single vacuum source is used to draw air from each of the vacuum ports, larger recording media is held more firmly against the media support surface than smaller recording media because the larger recording media covers more of the vacuum ports or grooves. Analogously, smaller recording media is held less firmly against the media support surface than larger recording media because of the air loss through the vacuum ports or grooves not covered by the smaller recording media, or a drop in vacuum caused by constant cross-section groove drag and loss. This may become problematic when the recording media comprises a flat aluminum plate or the like which is to be held on a curved media support surface, since the vacuum forces required to hold the aluminum plate firmly against the media support surface may be quite substantial.
Many attempts have been made to provide a vacuum system capable of providing a sufficient vacuum for different size recording media. One such technique is described in U.S. Pat. Nos. 6,133,936 and 6,047,733, both incorporated herein by reference in their entirety. This technique employs a sequencing manifold to selectively draw a vacuum through a plurality of individually addressable vacuum sections depending on the size of the recording media. Unfortunately, such a vacuum and manifold system, although quite effective, is generally highly complex and expensive to produce.
The present invention provides a method and apparatus for holding recording media against an external drum media support surface of an external drum system using an arrangement of variable cross-section vacuum grooves.
Generally, in accordance with a preferred embodiment, the present invention provides an apparatus comprising:
an external drum media support s urface; and
at least one variable depth vacuum groove in the media support surface.
Preferably, each vacuum groove has a continuously decreasing depth along its length, wherein the vacuum groove has a maximum depth adjacent a vacuum port and a minimum depth at a distal end of the vacuum groove. However, the depth of each vacuum groove may comprise, e.g., a series of stepped sections each having a gradually reduced depth. Other variable depth vacuum groove configurations are possible without departing from the scope of the present invention.
The present invention additionally provides a method for holding media on an external drum media support surface, comprising the steps of:
positioning the media over at least one variable depth vacuum groove in the media support surface; and
applying a vacuum to the vacuum grooves.
Even more generally, the present invention provides an external drum imaging apparatus comprising:
external drum support surface; and
at least one variable cross-section vacuum groove in the support surface.
The variable cross-section of each vacuum groove may be provided using any suitable method that provides a cross-section that decreases from a maximum adjacent a vacuum source/port to a minimum at a distal end of the vacuum groove. For example, as detailed above, a variable cross-section may be provided by varying the depth of the vacuum groove along its length (constant width). Alternately, a variable cross-section may be provided by varying the width of the vacuum groove along its length (constant depth). Further, a variable cross-section may be provided by varying both the depth and width of the vacuum groove along its length. Many other techniques or combination of techniques are also possible without departing from the scope of the present invention.
The present invention additionally provides an external drum imaging system comprising:
an external drum media support surface for supporting a supply of recording media;
at least one variable cross-section vacuum groove in the media support surface;
a system for applying a vacuum to each vacuum groove to hold the recording media against the media support surface; and
a system for recording image data onto the recording media.